Putty for AC lines

Just wondering - what do the HVAC folks use to caulk around the refrigerant lines where they enter the house? The stuff they use here in the midwest feels a lot like plumber's putty - never hardens, and you can kind of smoosh it around if part of the hole in the siding is exposed.

In my situation, it has pulled away too much to put back into place, and I'd like to add some more. I haven't seen any non-hardening caulk or putty at the store, other than plumber's putty -- should I use that?

No, don't use plumbers putty. I don't know what you call what you are describing, but it is available in most big box stores. It comes as a 1"x2"x6" grey colored "brick" wrapped in heavy clear poly. I think you may find it in the electrical dept. as it's used to seal electrical conduit penetrations as well.